为什么没有这种“绑定”的代码按预期方式工作的JavaFX的？

Question

我是新来的JavaFX。我无法理解为什么下面的代码无法正常工作。

import javafx.util.Sequences;

def nums = [1..10];
var curr = 0;

var evenOrOdd = bind if (nums[curr] mod 2 == 0) "{nums[curr]} is an even number" else "{nums[curr]} is an odd number";

for (curr in [0..(sizeof nums -1)])
{
    println("{evenOrOdd}");
}

我正在

1 is an odd number
1 is an odd number
1 is an odd number
1 is an odd number
1 is an odd number
1 is an odd number
1 is an odd number
1 is an odd number
1 is an odd number
1 is an odd number

如果我更改代码以

import javafx.util.Sequences;

def nums = [1..10];
var curr = 0;

var evenOrOdd = bind if (nums[curr] mod 2 == 0) "{nums[curr]} is an even number" else "{nums[curr]} is an odd number";

for (i in [0..(sizeof nums -1)])
{
    curr = i;
    println("{evenOrOdd}");
}

我得到正确的输出：

1 is an odd number
2 is an even number
3 is an odd number
4 is an even number
5 is an odd number
6 is an even number
7 is an odd number
8 is an even number
9 is an odd number
10 is an even number

显然，在循环计数器增量不被视为一个值变化和结合表达不重新评估。

任何人都可以解释这种行为背后的概念？

Answer 1

在为的表达含蓄地定义了它的迭代变量（这就是为什么你没有需要申报的 I 的在你的第二个例子）。即使已经存在具有相同名称的变量，为的仍然会创造它的范围一个新的。您的结合表达结合至 CURR 变量以外的的的循环，而不是内部的一个的的的环。和你的循环中的一个外不改变，所以结合的表达不会改变。

实施例以证明此行为：

var curr = 0;
var ousideCurrRef = bind curr;
println("Before 'for' loop: curr={curr}");
for (curr in [0..3])
{
    println("In 'for' loop: curr={curr} ousideCurrRef={ousideCurrRef}");
}
println("After 'for' loop: curr={curr}");

此将打印：

Before 'for' loop: curr=0
In 'for' loop: curr=0 ousideCurrRef=0
In 'for' loop: curr=1 ousideCurrRef=0
In 'for' loop: curr=2 ousideCurrRef=0
In 'for' loop: curr=3 ousideCurrRef=0
After 'for' loop: curr=0

因此， CURR 外的的的循环不会如果修改的的的循环内的相同名称的变量发生变化。